1. Field of the Invention
The present invention relates to a laser-marking laminated structure, and a laser-printed laminated structure. More specifically, the present invention relates to a laser-marking laminated structure, capable of being printed at a high printing speed by irradiation with a laser beam to form a clear image having excellent weather resistance, scratch resistance, water resistance and chemical resistance, and a laser-marked laminated structure obtained by printing an image on the laminated structure.
2. Description of the Related Art
Conventional printing methods include, for example, a first printing method that transfers a solution type ink to an image carrying medium by a printing plate bearing a relief, intaglio or planographic printing surface and dries the printed ink, a second printing method that prints images by a thermal transfer system using an ink ribbon and a thermal transfer printer, and a third printing method that prints images by jetting particles of liquid ink through fine nozzles.
These conventional printing methods, however, are encountered by difficulties in dealing with progressively increasing process speed of production lines, job shop type production and demand for labor saving in, for example, printing manufacturing date, quality guarantee limit date, lot number, plant name and such on product labels, cartons or plastic pouches in contents filling and packaging lines.
More specifically, the first printing method requires much labor for maintenance work for changing the printing plate, replenishing the printer with the ink and controlling the viscosity of the ink. Since the ink takes much time for drying, there is a limit to the first method in application to high-speed production lines and problems are liable to arise in the adhesion and abrasion resistance of the printed ink.
The second printing method does not use liquid ink and hence does not need any work for the control of the viscosity of the ink and time for drying the printed ink, However, the ink ribbon needs to be changed and hence the method is not necessarily satisfactory in application to a high-speed production line. Moreover, there are restrictions on the shape of image carrying mediums which can be printed by the second printing method and needs an increased printing cost.
The third printing method is capable of meeting requirements of high-speed printing and of clear printing. Therefore, the third method is capable of dealing with high-speed production lines. However, the use of the liquid ink in a production line is undesirable in view of maintaining a sanitary environment, the third method has problems in the facility of maintenance work including ink changing work, the nozzles of the ink-jet print head are liable to be stopped up with the ink and the percentage of defective prints is liable to increase.
Those disadvantages of the conventional printing methods become conspicuous particularly when the image carrying medium is a product label to be attached to a bottle for containing a liquid, such as water, a beverage or an alcoholic drink. Generally, a bottling line for bottling a beverage or the like operates at a high process speed and, in many cases, hot contents are bottled in the bottling line. After being filled with the contents, sealed and labeled, bottles strike together while being conveyed. In some cases, the bottles are coated with a bottle protecting liquid or immersed in cold water to cool the contents, and hence the product labels also are exposed to such severe conditions Therefore, printed portions of the labels need to be capable of withstanding such severe conditions.
The following methods, by way of example, have been proposed and put to practical use to indicate the month and year of manufacture of the bottled beverage and the like on a product label meeting such a requirement. A first method prints items to be indicated including months and years together with patterns in the periphery of a product label beforehand, and forms notches in portions of the product label in which relevant items are printed (clips off portions of the product label in which relevant items are printed) when filling a bottle bearing the product label with a beverage or the like. A second method forms a layer of a laser-coloring ink in an indicating area of a product label by printing, and irradiates the indicating area with a laser beam to print relevant items in the indicating area. A third method forms a layer of a laser light absorbing color ink which absorbs laser light, generates heat and decomposes upon absorption of the laser light and disappears in an indicating area of a product label, and irradiates the indicating area with the laser beam to remove portions of the layer of the laser beam absorbing color ink corresponding to a relevant image including characters and/or patterns so that the image is indicated in the color of a support element (paper sheet) of the product label in contrast with the color of the laser light absorbing color ink.
Those previously proposed techniques of indication and printing still have problems. For example, when notches are formed in the product label (when portions of the product label are clipped off), clippings are produced and the product label is liable to be torn from notched portions after being attached to a bottle.
Although the method that prints an indicating area with the laser-coloring ink and irradiates the indicating area with a laser beam to form characters and patterns by making the laser-coloring ink develop a color is suitable for high-speed printing, the laser-coloring ink is inferior in light fastness and chemical resistance. Particularly, the laser-coloring ink discolors when exposed to ultraviolet rays. Moreover, this method needs the regulation of the output of a laser. When the product label has an overcoating layer and the product label is irradiated with an excessively intensive laser beam, the overcoating layer is destructed and printed characters and patterns fade away when a bottle protecting liquid is applied to the product label.
Although the third method, which forms a layer of a laser light absorbing color ink which absorbs laser light, generates heat and decomposes upon absorption of the laser light and disappears in an indicating area of a product label, and irradiates the indicating area with the laser beam to remove portions of the layer of the laser light absorbing color ink corresponding to a relevant image so that the relevant image is indicated in the color of the support element (paper sheet) of the product label in contrast with the color of the laser light absorbing color ink, is suitable for high-speed printing, the clearness of the thus printed image is not somewhat unsatisfactory, and the scratch resistance and water resistance of the printed portions of the product label are not high enough to withstand severe conditions because portions of an overcoating layer and the ink layer are removed completely.
Accordingly, it is an object of the present invention to provide a laser-marking laminated structure, capable of developing a clear image excellent in scratch resistance, water resistance and chemical resistance at a high printing speed when irradiated with a laser beam.
Another object of the present invention is to provide a printed laminated structure obtained by irradiating a laser-marking laminated structure, capable of developing a clear image excellent in scratch resistance, water resistance and chemical resistance at a high printing speed when irradiated with a laser beam.
The inventors of the present invention made earnest studies to solve the foregoing problems and have made the present invention on the basis of the following findings obtained by the studies.
When a laminated structure having at least a support element, a base layer having a first color formed on a surface of the support element, and a laser light absorbing masking layer having a second color distinctly different from the first color in lightness and formed on the base layer, such as a white ink layer and a black ink layer, or a black ink layer and a silver ink layer, is irradiated with a laser beam of an appropriate intensity from the side of the laser light absorbing concealing layer to remove portions of the laser light absorbing masking layer corresponding to a desired pattern including characters, the pattern can clearly be displayed by distinct color contrast between the base layer and the masking layer, and the base layer remaining on the support element protects the support layer and, therefore, both the pattern and the support layer are resistant to various detrimental actions.
According to a first aspect of the present invention, a laser-marking laminated structure comprises, as essential components, a support element, a base layer formed on a surface of the support element, and a masking layer which can be decomposed and removed by irradiation with a laser beam, formed on the base layer.
According to the present invention, the base layer and the masking layer may be colored layers of colors distinctly different from each other in lightness, the base layer may be of a multilayer structure having at least an upper base layer and a lower base layer, the upper base layer may have a laser light absorptive power, and the lower base layer may be colored in a color similar to that of the upper base layer and capable of transmitting laser light.
According to the present invention, the masking layer may be an ink layer containing a metal powder.
According to the present invention, the base layer may be a two-layer layer structure having an upper base layer and a lower base layer, the upper base layer may be an ink layer containing carbon black, and the lower base layer may be an ink layer containing a coloring matter other than carbon black.